Dichter



United States Patent O ELECTROSTATIC LENS Qhanning Dichter, Syracuse, N. Y., assignor to General Electric Company, a corporation of New York Application April '3, 1953, Serial No. 346,673

6 Claims. (Cl. 313-82) The present invention relates. to improved electrostatic lenses and more particularly to an improved electron gun including an electrostatic lens.

Many commercially available television picture tubes employ an electrostatic, lens including three lens members which are rotationally symmetrical about the axis of the electron beam to be focused and axially spaced along such a beam. The intermediate member is often operated at a low potential such as zero or cathode potential while the end members of the lens are operated at a high positive potential such as the final anode potential. If such a potential relationship is contemplated, the first lens member may be mounted directly on the final anode of the electron gun.

While lens structures of this general type have been employed with reasonable success there has been considerable trouble from the standpoint of focusing of adequate quality in the application of these tubes. Some of the difiiculties are traceable to variations in dimensions as between guns of a given design and some difficulties are attributable to variations in circuit conditions in which the tubes are applied with respect to. the specific conditions for which the guns are designed and tested. Regardless of the source of these difiiculties, it has become apparent that a gun design which is less sensitive to variations of the type noted would be very desirable, and the present invention has for an important object the provision of an improved electrostatic lens structure ofiering better focusing under different conditionsof voltage in the application circuits and less susceptible to poor focusing as the result of variations in dimensions and spacings as between difierent lenses of the same design which are bound to occur in a mass production operation.

Further objects and advantages ofthe present invention will become apparent as the following description proceeds, reference being had to the accompanying drawing, and its scope will be pointed out in the appended claims. In the drawing,

Fig. 1 is an elevational view of a gun structure and. lens embodying my invention;

Fig. 2 is an enlarged sectional view of the structure shown in Fig. 1; and

Fig. 3 is a sectional view taken along the line 3-3 of Fig. l.

Referring now to Fig. l of the drawing, I have shown my invention embodied in a focusing structure including an outer focusing cylinder 1, a similarly shaped inner focusing member 2, and an intermediate focusing member 3. These focusing. members are rotationally symmetrical and are supported in spaced and insulated relation with respect to one another and in spaced relation along the axis .of a beam to be focused by means of a plurality of glass stalks 4 in which are embedded studs 5. These studs are welded at the other ends thereof to the focusing electrodes in accordance with common practice.

The focusing structure formed by these three electrodes is supported directly from afinal anode 6 by means of mating flanges 2a and 6a formed respectively on the 2,732,511 Patented Jan. 24,-, 1956 focusing member 2 and the anode 6. In addition to the anode 6 the gun includes an accelerating grid 7 a control grid-cathode assembly 8 including a grid cup 9. The anode 6 and grids 7 and 9 are supported in spaced and insulated relation by glass stalks 10 and studs 11 in the same manner as described in connection with the focusing members 1-3, inclusive. The entire gun and lens assembly may be supported from the glass stem 12. of a cathode ray tube and the lead-in conductors 13-18, inclusive, sealed therethrough by means of various conductors connected between these lead-in conductors and the electrodes.

As will be readily appreciated by those skilled in the art, lateral support for the gun assembly may be provided by suitable spring contact fingers or snubbers (not shown) supported from a flange 19 at the outer end of the focusing member- 1 and engaging the wall of the tube envelope. In addition to lateral support, these fingers also maintain the focusing members 1 and 2 and the final anode 6 at the potential of the tube wall coating which, in accordance with usual practice, is the final anode potential of the tube. From an inspection of Fig. 1, it is seen that the control grid cylinder 9 is connected to lead-in conductor 13 by a conductor 13a, accelerating grid 7 is connected to lead-in conductor 18 by a conductor 18a, focusing electrode 3 is connected to lead-in conductor 16 by a conductor 16a, lead-in conductors 14, 15 are connected with the heater element terminals 14a and 15a, and lead-in conductor 17 and conductor 17a provide a cathode connection.

The detailed construction of the various elements of the gun and lens structure and their. functioning will be better understood by a consideration of the enlarged sectional view of Fig. 2. The grid. member 9 is in the form of a cup shaped member having a beam aperture 20. A cathode sleeve 21 is. supported within the control grid cylinder 9 by means of an insulating disk support 22 with. the end of the cylinder directly behind beam aperture 20.

The grid cylinder is provided with an area of, reduced thickness surrounding the grid aperture 20 and the end wall is crimped as shown at 23 to increase the rigidity thereof. A support and spacing member or collar 24 is positioned between the insulating disk 22 and the grid cylinder and engages. the grid cylinder just inside of the corrugation or ridge to lend additional support to the central area of the grid. This construction serves to provide a thinner grid wall surrounding the grid aperture which results in or makes possible a greater grid-to-cathode spacing for the same grid aperture diameter, control grid to accelerating grid spacing and cutoff voltage. Since grid-to-cathode shorts have been a considerable cause of shrinkage, this feature makes possible an improved tube from the manufacturing standpoint without any sacrifice in its control charactelistics. The grid construction just described is fully disclosed and claimed in my copending application Serial No. 346,674 filed concurrently herewith and assigned to the assignee of this application.

The beam produced by the grid-cathode assembly passesthrough an aperture 25 in accelerating grid 7 and as the beam passes from the region of the accelerating grid to the final anode 6. it is subjected to a transverse component of electrostatic field caused by the bias slot between these electrodes. As well understood by those skilled in the art, a counter deflection force of equal magnitude with respect to the electrons is provided by a so-called ion trap magnet (not shown) at this region to maintain the electrons substantially on the axis of the anode cylinder 6. The ions, being less affected by the magnetic field thanv by the electrostatic field, proceed to the right and, are collected on the wall of the anode 6, or some part of the metal structure of the gun. Since the counteraction of the electric and magnetic fields with respect to the electrons is not exactly equal point by point along the beam, electrons actually do move to the right of the axis under the action of the electrostatic field and are then returned by the magnetic field. This would tend to make the beam cross the axis again at a long angle.

However, as will be noted from the drawing, the base of the gun structure is ofiset to the left or, in other words, inclined slightly to the axis of the tube envelope (not shown) and to the axis of the exit end of the anode. With this geometry of the parts electrons that move slightly to the right of the axis in passing between the grid 7 and anode 6 may be returned to the axis of the exit end of the anode by the action of the magnetic field.

The focusing structure which forms the subject of the present invention will now be described in detail. The end focusing members 1 and 2 are rotationally symmetrical and are generally similar in configuration but oppositely directed, i. e., the exit end of the inner focusing member 2 is in proximity to the entrance end of the outer focusing member 1 and is similarly shaped. As illustrated, each focusing member includes a cylindrical portion 27 slightly smaller than the body of these members and is provided with beam defining portions 28 formed by a cylindrical wall of substantially smaller diameter than the portions 27. These beam definin passages are supported from the portions 27 by sections 29 of reverse curvature. From one point of view, the ends of the focusing members may be considered as including re-entrant cylindrical portions connected to the body of the focusing members by an inwardly directed portion including sections of reverse curvature. This particular configuration provides for a very desirable field distribution in cooperation with the surrounding intermediate focusing member 3. Also, the curved portions tend to reduce voltage gradients and in this way limit the distorting effect of secondary electrons which are quite marked instructures where high gradients exist and secondaries are emitted in considerable numbers. The shape of the ends of the end focusing members corresponds generally with the equipotential surface at the end of a cylindrical lens member without any end member. It will be noted that the ends 30 of the surrounding intermediate lens member 3 are also rounded oif to prevent high voltage gradients between it and the lens members 1 and 2. The shape of the field is also controlled somewhat by the dimensions of the focusing electrodes and the amount of insertion of the end electrodes into the intermediate electrode. The difference in radii between the end focusing members and the intermediate electrode is equal to or less than the amount of insertion of the end focusing members into the intermediate focusing member. In other words, the distance y is equal to or greater than the distance x.

While the exit opening defined by the ring 28 of the focusing member 2 may be utilized as a limiting aperture it is even more desirable to provide the limiting aperture in a totally field-free region so that no distortion due to secondaries, which might tend to be accelerated if the aperture were in a strong field, is caused. Accordingly, a cup-shaped member 31 is positioned Within the focusing member 2 with the closed end thereof resting on a shoulder 32 provided between the body and portion 27 of reduced section. The closed end is provided with limiting aperture and is preferably spaced from the focusing aperture by a distance at least equal to the diameter of the focusing aperture. As illustrated, this cup-shaped member 31 extends slightly into the end of the final anode 6 and positions the focusing electrode with respect thereto. Focusing electrode 2 and anode 6 are secured together by welding the flanges 2a and 6a. An exit aperture 34 in the focusing electrode 1 is defined by an inwardly directed flange 35 on the member 19.

While I have described a particular embodiment of my invention it will be apparent to those skilled in the art that changes and modifications may be made Without departing from my invention in its broader aspects and I aim, therefore, in the appended claims to cover all such changes and modifications as fall Within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An electrostatic lens system comprising three coaxial electrode members, said members including an intermediate cylinder and a pair of end cylinders, said end cylinders each having a portion received within said intermediate cylinder and insulated therefrom, said electrode members being cooperable to provide an electrostatic field, one of said end cylinders including an apertured end Wall defining a beam passage, and said end wall having a surface shaped to correspond generally to an end portion of said electrostatic field.

2. An electrostatic lens system comprising three coaxial electrode members, said members including an intermediate cylinder and a pair of end cylinders, said end cylinders each having a portion of reduced diameter extending a predetermined distance into said first member and insulated therefrom, said electrode members being cooperable to provide an electrostatic field, one of said end cylinders including an apertured end wall defining a beam passage, and said end wall having a surface shaped to correspond generally to an end portion of said electrostatic field.

3. An electrostatic lens system comprising three coaxial electrode members, said members including an intermediate cylinder and a pair of end cylinders, said end cylinders each having a portion received Within said intermediate cylinder and insulated therefrom, said electrode members being cooperable to provide an electrostatic field, adjacent ends of said end cylinders each having an apertured end wall defining a beam passage, and said end walls having surfaces shaped to correspond generally to the end portions of said electrostatic field.

4. An electrostatic lens system comprising three coaxial electrode members, said members including an intermediate cylinder and a pair of end cylinders, said end cylinders each having a portion received within said intermediate cylinder and insulated therefrom, said electrode members being cooperable to provide an electrostatic field, one of said end cylinders including an apertured end wall defining a beam passage, said end wall having a surface shaped to correspond generally to an end portion of said electrostatic field, and said end wall further including a re-entrant portion of reverse curvature with respect to said field.

5. In combination, electron beam producing means, and an electrostatic lens system comprising three electrode members spaced axially along the path of an electron beam, said members including an intermediate cylinder and a pair of end cylinders, said end cylinders each having a portion received within said intermediate cylinder and insulated therefrom, said electrode members cooperating to provide a beam focusing electrostatic field, one of said end cylinders including an apertured end wall defining a focusing aperture, said end Wall having a surface shaped to correspond generally to an end portion of said electrostatic field, and a member defining a beam limiting aperture positioned in said last-mentioned end cylinder at a distance from said focusing aperture at least equal to the diameter of said focusing aperture.

6. An electrostatic lens system comprising three coaxial electrode members, said members including an intermediate cylinder and a pair of end cylinders, said end cylinders each having an end portion received within said intermediate cylinder and insulated therefrom, said end portions being of substantially smaller diameter than said References Cited in the file of this patent UNITED STATES PATENTS Keyston et al. July 5, 1938 Jefele et a1. Oct 8, 1940 Boeing Jan. 27, 1953 Giacchett May 12, 1953 

